On the IP network adopted for the Internet or LAN, the TCP protocol is commonly employed as a reliable communication protocol in various applications such as e-mail and a Web browser. The TCP protocol is standardized as RFC (Request for Comments) 793.
According to the TCP protocol, a process called 3WHS (3 Way Handshake) is executed when establishing a connection. In the 3WHS process, SYN, SYN ACK, and ACK packets are exchanged between a client and a server. Data are not transferred until the 3WHS process is completed.
In transaction-type (connection-oriented) communications via a protocol such as HTTP (Hyper Text Transfer Protocol) used for WWW (World Wide Web) and TCP, connect time per communication is generally short, and the 3WHS process constitutes a large portion of the cost. That is, the 3WHS process is performed with large overhead to the packets that are needed to transmit data, and also requires extra time to exchange packets for 3WHS. This is a serious problem for devices such as cellular phones that use wireless channels with narrow bands and long delay.
The T/TCP protocol is a protocol proposed to circumvent the 3WHS process in the TCP protocol, and defined by RFC1644. T/TCP circumvents the 3WHS by adding a serial number called CC (Connection Count) to the packet on each session. Therefore, the T/TCP protocol has the advantage over the TCP protocol in transmission speed and network traffic.
As is mentioned above, there are following problems in conventional IP network communications.
First, since the T/TCP protocol is not prevalent in the present circumstances, communication devices in general use are compatible only with the TCP protocol and there are few devices compatible with the T/TCP protocol. Besides, in order to establish communication via T/TCP, it is necessary that both sending device and receiving device are compatible with T/TCP. Even if either one of devices is compatible with T/TCP, the merit of T/TCP cannot be obtained. Consequently, in communication devices that are compatible with T/TCP, T/TCP is often disabled by default, and the T/TCP protocol has been hardly employed so far.
Second, in conventional communications via T/TCP, it is impossible to apply NAT (Network Address Translation).